/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.db.metadata.rescon;

import org.apache.iotdb.db.conf.IoTDBDescriptor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.atomic.AtomicLong;

public class MemoryStatistics {

    private static final Logger logger = LoggerFactory.getLogger(MemoryStatistics.class);

    /**
     * threshold total size of MTree
     */
    private long memoryCapacity;

    private final AtomicLong memoryUsage = new AtomicLong(0);

    private volatile boolean allowToCreateNewSeries;

    private static class MemoryStatisticsHolder {

        private MemoryStatisticsHolder() {
            // allowed to do nothing
        }

        private static final MemoryStatistics INSTANCE = new MemoryStatistics();
    }

    public static MemoryStatistics getInstance() {
        return MemoryStatisticsHolder.INSTANCE;
    }

    private MemoryStatistics() {
    }

    public void init() {
        memoryCapacity = IoTDBDescriptor.getInstance().getConfig().getAllocateMemoryForSchemaRegion();
        memoryUsage.getAndSet(0);
        allowToCreateNewSeries = true;
    }

    public boolean isAllowToCreateNewSeries() {
        return allowToCreateNewSeries;
    }

    public boolean isExceedCapacity() {
        return memoryUsage.get() > memoryCapacity;
    }

    public long getMemoryCapacity() {
        return memoryCapacity;
    }

    public long getMemoryUsage() {
        return memoryUsage.get();
    }

    public void requestMemory(long size) {
        memoryUsage.getAndUpdate(v -> v += size);
        if (memoryUsage.get() >= memoryCapacity) {
            logger.warn("Current series number {} is too large...", memoryUsage);
            allowToCreateNewSeries = false;
        }
    }

    public void releaseMemory(long size) {
        memoryUsage.getAndUpdate(v -> v -= size);
        if (!allowToCreateNewSeries && memoryUsage.get() < memoryCapacity) {
            logger.info("Current series number {} come back to normal level", memoryUsage);
            allowToCreateNewSeries = true;
        }
    }

    public void clear() {
        memoryUsage.getAndSet(0);
        allowToCreateNewSeries = true;
    }
}
